Preparation of metal fluoborates



United States Patent PREPARATION OF METAL FLUOBORATES Albert D. McElroyand Richard Hunt, Evans Qity,

Pa., assignors to Gallery Chemical Company, Pittsburgh, Pa., acorporation of Pennsylvania No Drawing. Application April 12, 1954,Serial No. 422,648

11 Claims. (Cl. 204-159) This invention relates to an electrochemicalmethod of preparing metal fiuoborates.

Metal fiuoborates were first prepared by the reaction of a metalcarbonate with fluoboric acid. Lithium and aluminum fiuoborates areformed as by-products in the reaction of lithium aluminum hydride withboron trifluori-de ethyl etherate but the main product is diborane.Similarly, sodium and potassium fiuoborates are produced as by-productsin the preparation of diborane from sodium and potassium borohydridesand boron trifluoride. In the production of diborane it is necessary torecover BFs from the fiuoborates which are produced as by products ofreaction. Sodium and potassium fiuoborates decompose to produce BF3 whenheated to a very high temperature. Other fiuoborates, such as alkalineearth fiuoborates decompose to produce BF3 at a much lower temperature.It has therefore become important to provide a method for readilyconverting sodium and potassium fiuoborates to less stable fiuoborates.

It is one of the objects of this invention to provide a new and improvedmethod for the preparation of metal fiuoborates in substantial yieldsfrom readily available fiuoborates such as sodium or potassiumfluoborate.

Another object of this invention is to provide a new and improved methodfor preparing metal fiuoborates from sodium fiuoborate by electrolysis.

A further object is to provide a new and improved method for preparingmetal fiuoborates in which sodium fluoborate is dissolved in anon-aqueous solvent and electrolyzed using a mercury or platinum cathodeand a sacrificial metal anode.

Other objects of this invention will become apparent throughout thespecification and claims as hereinafter related. This process will bedescribed more fully in the specification and the novelty thereof willbe particularly pointed out and distinctly claimed.

In this invention, a solution of an ionic fluoborate MBF4 in an ionizingnon-aqueous solvent is electrolyzed using either a mercury cathode or aninert cathode and a sacrificial metal anode comprised of the metal (M ofthe fluoborate desired. The metal M of the dissolved fluoborate isdeposited at the cathode as an amalgam if a mercury cathode is used. Themetal M must form an amalgam less readily than does metal M. At the sametime the metal M ions will go into solution from the anode. If theresultant fluoborate M BF4 is soluble in the solvent, the reaction willgo to completion only if the amalgam of the metal M is higher in theelectromotive series for the solvent used than the M amalgam. If thedesired fluoborate M BFi is substantially insoluble in the solvent the Mand BE; ions will immediately react to precipitate M BF4 at the anode.

In a particular experiment, 300 ml. of a saturated solution of sodiumfluoborate in tetraethyleneglycol dimethyl ether [CH3(C2H4O)4OCH3] waselectrolyzed between a magnesium anode and a platinum cathode. A totalof 0.5 amp. current with 30 applied volts was passed at an anode currentdensity of ma. per cm The temperature of the cell during theelectrolysis was approximately 30 C. A deposit of metallic sodium wasobserved at the cathode and a gelatinous precipitate, magnesiumfluoborate, deposited in the cell during the electrolysis. In otherexperiments it has been found that this reaction proceeds moresatisfactorily with a mercury cathode which forms an amalgam with thedischarged sodium. By the use of a mercury cathode it has been foundpossible to prepare fiuoborates of metalswhich are normally lower in theelectromotive series than sodium.

Other experiments indicate that substantial yields of fiuoborates may beobtained by using various polyethylene glycol ethers [RO(CzH4O)1.R,where R is an alkyl group and n is an integer] or lower organic aminessuch as ammonia, methylamine, ethylamine and dimethylamine as solvents.By judicious selection of the electrolytic solvent the resultingfluoborate may be obtained either as the anhydrous salt or as a solvate.Selection of the solvent to be employed in a particular instance will begoverned by the extent and nature of solvation which can be tolerated inthe product.

Metals which may be used as anodes include any desired metal the amalgamof which is more electropositive than sodium amalgam or whose fiuoborateis insoluble in the solvent used for the electrolysis. It is alsopossible to use fiuoborates of metals other than sodium as the solute inthis process. The necessary requisites are that the dissolved fiuoboratemust dissociate .ionically in the solvent and the resultant fiuoboratemust be insoluble in the solvent or the amalgam of the metal anode mustbe more electropositive than the amalgam of the metal deposited byelectrolysis of the dissolved fiuoborate. The term more electropositiveas used herein is used in the sense that one metal is moreelectropositive than another metal when the one metal .is less noblethan the other metal and stands higher than the other metal in theelectromotive series for the particular solvent in which thedetermination of electrochemical activity was made. It is to beunderstood that because of the diiferent solvation energies of metalions in diflerent solvents the relative order of metals in theelectromotive series varies slightly from one solvent to another. It isapparent therefore that, subject to the aforementioned requisites, thisprocess may be employed as a method of preparation of any desired metalfluoborate from another metal fluoborate.

While we have described a few embodiments of our invention it is to beunderstood that within the scope of the claims appended hereto thisinvention may be practiced otherwise than as specifically described.

Having thus described our invention what we desire to claim and secureby Letters Patent of the United States is:

l. A method of preparing metal fiuoborates comprising electrolyzing anon-aqueous solution of an ionic metal fiuoborate with an anode of thedesired metal in a solvent in which the desired metal fluoborate issubstantially insoluble and recovering the fluoborate precipitated atthe anode.

2. A method according to claim 1 in which the nonaqueous solvent is of.the group consisting of polyethyleneglycoldialkylethers, liquid ammonia,and lower organic amines.

3. A method according to claim 1 in which the nonaqueous solvent is apolyethyleneglycol dialkyl ether.

4. A method according to claim 1 in which the nonaqueous solvent isliquid ammonia.

5. A method according to claim 4 in which non-aqueous solvent is a lowerorganic amine.

6. A method according to claim 1 in which the ionic metal fiuoborate isof the group consisting of sodium fluoborate and potassium fiuoborate.

7. A method according to claim 1 in which the anode is comprised ofametal which is less noble than the metal of the dissolved fluoborate.

8. A method according to claim 7 in which the cathode is mercury.

9. A method of preparing metal fluoborates comprising electrolyzing anon-aqueous solution of an ionic fluoborate having the general formulaMBF4, where M is a. metal whose fluoborate is soluble in the solvent,using a mercury cathode and a sacrificial metal anode of a metal M,where M is the desired metal ion and forms an amalgam less readily thanM, to produce the desired metal fluoborate M BFo and (M) amalgam, andrecovering the fluoborate thus formed.

10. A method according to claim 9 in which the desired fluoborate M BF4is insoluble in the solvent.

11. A method of preparing magnesium fluoborate com- References Cited inthe file of this patent UNITED STATES PATENTS Lowe et al Mar. 30, 1954Szekely Sept. 28, 1954 OTHER REFERENCES Journal of The American ChemicalSociety, vol. 41 (1919), pages 1769-1776, paper by Browne et a1.

Principles of Electroplating and Electroforming, by Blum et 211., 3rdedition (1949), page 45.

1. A METHOD OF PERPARING METAL FLUOBORATES COMPRISING ELECTROLYZING ANON-AQUEOUS SOLUTION OF AN IONIC METAL FLUOBORATE WITH AN ANODE OF THEDESIRED METAL IN A SOLVENT IN WHICH THE DESIRED METAL FLUOBORATE ISSUBSTANTIALLY INSOLUBLE AND RECOVERING THE FLUOBORATE PRECIPITATED ATTHE ANODE.